Two-part resin bonded cast metal bridges for use when abutment teeth have unequal effective root surface areas

Resin bonded cast metal bridges have become a popular method of replacing missing teeth. Such bridges are usually constructed as single castings following modifications to the abutment teeth in order to ensure a distinct path of insertion and to secure maximum metal to tooth contact. Unfortunately, long term retention of resin bonded bridges cannot be guaranteed and many surveys have reported substantial failure rates, particularly in the posterior segments of the mouth. It is the authors contention that many of these failures occur because clinicians are neglecting one of the fundamental principles of fixed bridge prosthodontics, namely that abutment teeth should be matched for effective root surface area (bony support). This article describes how problems created by incompatible abutment teeth can be overcome successfully by the construction of resin bonded bridges in two parts which are cemented separately, but interlock to provide a movable joint. Such an arrangement allows independent movement of the abutment teeth whilst providing sufficient retention and support for the bridge. The two-part design can also overcome problems created by malaligned abutment teeth as well as allowing conventional full crown retainers to be combined with resin bonded retainers.